Container bodymaker



April 1970 A. T. L. AUSTING 3,508,507

CONTAINER BODYMAKER Filed Sept. 8, 1967 3 Sheets-Sheet 2 F/G.2 FIG.3

1NVENTOR. AUGUST THEODORE LESTER AUSTING ATTORNEY April 1 A. T. L. AUSTING 3,508,507

. CONTAINER BODYMAKER Filed Sept. 8, 1967 3 Sheets-Sheet 5 INVgNTOR. AUGUST THEODORE LESTEI; AUSTING BYgM4/%%/% ATTORNEY United States Patent O 3,508,507 CONTAINER BODYMAKER August Theodore Lester Austing, Geneva, N.Y., assignor to American Can Company, New York, N.Y., a corporation of New Jersey Filed Sept. 8, 1967, Ser. No. 666,408 Int. Cl. B2ld 51/26 US. Cl. 113--12 8 Claims ABSTRACT OF THE DISCLOSURE In a can bodymaking machine, a bumping hammer is held in sustained contact with a can body side seam during the formation of the latter to effect heat transfer from the side seam to the bumping hammer and thereby facilitate setting of the sealant used in the side seam.

BACKGROUND OF THE INVENTION A large proportion of the metal containers used for commercial backaging of foods, beverages, and other products consists of the familiar three-piece can having ends double-seamed to a can body, the latter usually including a lock and lap type side seam hermetically sealed by a metallic solder. Soldered can bodies are necessarily made from materials which are readily solderable, such as tin plate. More recently, some cans have been manufactured utilizing a lap type side seam bonded or cemented with an organic adhesive. This latter construction eliminates the requirement for a solderable body material and permits the use of other materials, such as tin-free steel and aluminum, for making seamed cans which are suitable for foods, beverages, and other products which may be required to withstand pressurized conditions.

Cemented can bodies are formed by applying an extruded adhesive ribbon to the marginal edge surface of a flat body blank, feeding the blank to a high-speed, automatic can bodymaker which heats the adhesive to a semi-fluid, tacky condition, rolls the blank into a generally cylindrical form, and presses the opposite longitudinal edges together with the tacky adhesive therebetween to form a bonded lap side seam. Pressing the edges together to form the seam is sometimes referred to as bumping. To make it possible to operate a can line of this type at commercially acceptable speeds, it is necessary to cool the adhesive rapidly at the bumping operation in order for the adhesive to set and thereby establish the integrity of the formed body. The speed of cooling may be enhanced by chilling the spline used to support the inside of the can adjacent the side seam and also by chilling the hammer used to press the lap seam against the spline. To further increase the rate of heat removal and thus increase production rates, means are provided, according to the present invention, to lengthen the period of time in which the chilled bumping hammer is held in contact with the lap seam without slowing down the speed of operation of the body-maker. In this regard, it is noted that in conventional apparatus used on soldered side-seam can bodies, the bumping hammer is actuated by an eccentric so that the hammer makes only momentary contact with the seam as the eccentric passes top dead center. In the illustrated embodiment of the instant invention, the period of contact time with the seam is increased by incorporating a cylinder-piston assembly into the hammer mechanism, the arrangement being such that the hammer is held in contact with the lap seam for a dwell period corresponding to a predetermined number of degrees or rotation of the eccentric on the hammer drive shaft. As a result, the chilled hammer and spline remain in heattransferring contact with the can body side seam for a 3,508,507 Patented Apr. 28, 1970 SUMMARY OF THE INVENTION In a can bodymaking machine having a mandrel supporting a partially formed one-piece cylindrical can body, a drive element, preferably an eccentric, is operable to vertically reciprocate a bumping hammer to bring it into engagement with the overlapped edges of a can body and thereby form them into a side sea-m. The hammer is mounted so that it engages the can body before the upward driving stroke of the drive element is completed, and a device, hereinafter called a dwell means is interposed between the drive element and the hammer to permit the drive element to overtravel while the hammer is held in sustained, substantially constant-pressured contact with the side seam for a predetermined length of time, called a dwell period. The bumping hammer and the spline on the can bodymaking machine are chilled to effect rapid heat transfer from the side seam during this dwell period to thereby facilitate setting of the sealant used in the side seam. Preferably, the dwell means comprises a cylinder element, a piston element, and a source of pressurized fluid communicating with said cylinder element to urge the piston element into an extended position. One of said elements is driven by the eccentric and the second of said elements is pivotally connected to the bumping hammer. After the hammer assembly closes the side scam, the element connected to the eccentric continues its cyclic movement as the hammer assembly to which said second element is connected temporarily remains at rest during the dwell period to provide the aforesaid sustained engagement, the relative movement between the two elements being accounted for by displacement of the piston in the cylinder.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is an elevational view, parts of which are broken away and in section, of the bumping station portion of a can bodymaker with the hammer in its down position.

FIGURE 2 is an elevational view similar to FIGURE 1 but showing the hammer in its up position.

FIGURE 3 is an elevational view, parts of which are broken away and in section, looking from the right-hand side of FIGURE 2.

FIGURE 4 is a partial elevational view, on a larger scale, of the hammer assembly looking substantially along the line 4-4 of FIGURE 2.

FIGURE 5 is an exploded view of the hammer assembly and hammer slide.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In manufacturing cans with bonded lap side seams, a thermoplastic or hot-melt cement is extruded or otherwise deposited in a semi-molten flowable condition on side-seam edge portions of a moving procession of coated, flat can body blanks. The blanks are then fed to a can bodymaker where the blanks are rolled and a lap side seam is formed by pressing the overlapping longitudinal edge portions together with the cement therebetween. This latter operation, sometimes hereinafter referred to as bumping, is performed at the bumping station of a can bodymaker. The drawings herein disclose principal parts of a side-seam assembly or bumping station adapted to be used with a can body-making machine, which may be of the type shown in US. Letters Patent 1,625,091 issued Aug. 17, 1927.

In such machine, a partially formed tubular sheetmetal can body B having a ribbon of a suitable thermoplastic adhesive A adjacent one longitudinal edge portion thereof is formed on a support mandrel and advanced therealong in a step-by-step or intermittent manner to the illustrated bumping station. The means for advancing the can bodies in succession along the mandrel 10 include reciprocal feed slide bars 11 and spring held feed dogs 12 mounted thereon, a detailed disclosure of such means being more particularly set forth in the aforementioned U.S. Patent 1,625,091.

After the can body B has been advanced along the mandrel 10 to the bumping station, it is securely clamped to the upper side of the mandrel 10 by the clamping member 13. At the bumping station, the mandrel 10 comprises a central body part 14, two side members or expanding cheeks 16, the aforementioned slide bars 11, and a rounded bottom spline against which the bumping is effected. The expanding cheeks 16 are held in collapsed position as the bodies B enter the bumping station, and are thereafter movable laterally to expanded position by a wedge bar 24, a rocker lever (not shown), and associated elements (not shown) which are known in the art, an example thereof being disclosed in U.S. Patent 1,770,041 issued July 8, 1930. When the expanding cheeks 16 are collapsed, as shown in FIG. 1, the sides of each can body B are slightly contracted to position the sideseam edge portions in the overlapping position of FIG. 1. Contraction of the can body sides may be effected by a plurality of flexible pressure members 26 arranged around the upper half of the expanding mandrel 10 and a pair of pivotally mounted pressure elements or fingers 28 adjacent the lower half of the mandrel 10. The arrangement and operation of these pressure elements and fingers are known in the art, and an example thereof is disclosed in U.S. Patent 2,563,805 issued Aug. 14, 1951.

The bodymaker parts and other elements thus far described and referred to by way of reference to issued patents are operable to position a partially formed can body into the position shown in FIG. 1 wherein overlapping but spaced longitudinal edges with hot melt adhesive A therebetween are disposed at the lower part of the mandrel 10 overlying a hammer assembly generally designated by the numeral 29.

The bumping or hammer assembly 29 bringing the overlapped body portions into contact with each other to thereby form them into closed and sealed can body side seam S comprises a hardened hammer blade 30 mounted in a slot 31 in a hammer body 32 and suitably secured in place by clamping screws 34. The hammer body 32 is, in turn, mounted and secured by clamping bolts 33 in a slot 35 in a hammer slide 36. The hammer slide 36 has a pair of arms, each carrying slide bearings 38 which slide on guide rods 40. The guide rods 40 are fixed to the machine frame 42 as shown in FIG. 1 and function to guide the hammer assembly 29 as it is cycled up and down.

The hammer assembly 29 is secured to the upper end of a dwell device which preferably takes the form of a cylinder-piston assembly indicated generally at 44, the latter being connected to a drive means in the form of an eccentric or crank 46 formed on a crankshaft 48 journaled on bearings 49 mounted on the machine frame 42. The crank 46 and cylinder-piston assembly 44, which utilizes a compressible fluid (e.g. air) as will be described, transmit the motion of the eccentric to the hammer assembly 29 to reciprocate it between its down (FIG. 1) position and its up (FIG. 2) position and to provide a dwell period to permit the hammer assembly 29 to remain in its up position for an appreciable interval so that the hammer blade 30 remains in sustained contact with each can body side seam for a predetermined number of degrees of rotational travel of the crankshaft 48. The hammer blade is cooled by a cooling medium, as will be described, so that during the dwell period when the hammer blade 30 is in contact with the can body side seam S, heat is transferred from the side seam S and from the adhesive A to the hammer blade 30 and to the cooling medium circulated therein to facilitate rapid setting of the adhesive A. It will be understood that during this time, the chilled spline 20 also removes heat from the side seam S.

Considering the hammer assembly 29 in greater detail, it includes a lifter pad 50 which is carried on a slide stem 52 (see FIG. 5) disposed in a vertical slideway 54 formed in one side of the hammer body 32. Lifter pads are known in the art, an example thereof being disclosed in the aforementioned U.S. Patent 2,563,805, and accordingly, only a brief description will be set forth herein. The normal position of the lifter pad 50 is that shown in FIG. 1 which the pad is set in extended position above the upper face of the hammer blade 30 by a resetting mechanism generally designated as 58, as will be described. When the hammer assembly 29 moves up toward the expanding mandrel 10, the extended lifter pad 50 engages the overlying portion of the can body Which will form the overlapped part of the side seam S and lifts it toward the underlying portion which will form the underlapped part of the side seam S.

At this stage in the cycle of operation of the machine, the cheeks 16 of the expanding mandrel 10 move outwardly under the action of the wedge bar 24, as disclosed in the aforementioned U.S. Patent 1,770,041, and the action expands the can body B to its full size. This expansion or sizing of the can body B takes place while the hammer assembly 29 continues to move up toward the mandrel 10 and while the pressure member 26 and the fingers 28 are holding the body B under spring pressure. After the lifter pad 50 has raised the overlying portion of the can body B as far as it will go, the lifter pad 50 remains stationary and the hammer blade 30 continues its upstroke, the result being that the pad 50 is moved to its down position, as shown in FIG. 2.

When the hammer blade 30 engages the overlapping longitudinal marginal edge portions of each can body B, it sequeezes them tightly against the mandrel spline 20 to form the side seam S. The hammer blade 30 strikes each body B with such force that it presses the adhesive A tightly against the underlap portion of the side seam and squeezes it out to some extent to distribute the adhesive throughout the side seam. As this happens, the hammer blade 30, along with the spline 20, extracts heat from the body and, by conduction, from the adhesive A, thus chilling the adhesive A below its melting point and setting it to form a tight seam, and to prevent it from opening up when the body B is removed from the bumping station.

On the downstroke of the hammer assembly 29, the lifter pad 50 is moved from its down position to its extended position by the resetting mechanism 58 which comprises a bell crank 60 suitably fixed to a shaft 62 mounted for relative rotation on a bracket 64 fixed to the hammer slide 36. One arm 66 of the bell crank 60 engages a lug 56 projecting from the slide stem 52, and the other arm 68 is adapted to be engaged by a cam element 70 fixed to the machine frame 42. A friction slip device comprising a coil spring 72 (FIG. 3), friction discs 73, and an adjustable collar 74, all carried on the shaft 62, functions to frictionally maintain the lifter pad 50 in either its extended (FIG. 1) position or its retracted position (FIG. 2) until it is positively moved to its other position. It will be apparent that on the down stroke of the hammer assembly 29, the crank arm 68 is engaged by the high part of the cam element 70 to reset the lifter blade 50 to its extended (FIG. 1) position, while on the upstroke of the assembly 29, the lifter blade 50 is moved from its extended position to its down position when it engages the side seam S.

High end straighteners, otherwise known as gauging fingers 78, are disposed at the ends of the central passageway 31 in the hammer body 32 and are normally extended above the hammer blade 30. At the start of the upstroke of the hammer assembly 29, the fingers 78 are temporarily angled outwardly or spread apart to straddle the overlapping edge portions of the can body B. Thereafter, during the upstroke of the hammer assembly 29 and prior to the contact of the hammer blade 30 with the can body B, the fingers 78 are cammed towards each other and into contact with the ends of the body to longitudinally align the overlap and underlap portions of the side seam S. Gauging fingers are known in the art, and an example thereof is disclosed in the aforementioned U.S. Patent 1,770,041. Briefly, each finger 78 is vertically and slightly laterally movable in guideways formed between the outer end walls 79 of the central passageway 31 in the hammer body 32 and the outer ends of the hammer blade 30, and each is frictionally pressed against the walls 79 at all times by contact pins 80 (FIG. 4) which are biased into engagement with the fingers 78 by coil springs 82. The fingers 78 are normally held in an upwardly extended (FIG. 1) position until they contact the bottom surface of the spline 20, at which time they are pushed into the hammer body 32 by the spline 20 as the hammer blade 30 continues its upstroke. When the fingers 78 are in their upwardly extended position, cam surfaces 81 which are formed on the outer end walls of the fingers 78 are raised above upper cam surfaces 83 on the outer end walls 79 of central passageway 31 and as a consequence, the fingers 78 are spread apart. However, as the fingers 78 move downwardly, the cam surfaces 81 engage the came surfaces 83 and thus move the fingers 78 toward each other, thus moving them into engagement with the edges of the body and thereby longitudinally gauging the can body B.

Each finger 78 is provided with an extension lug 84 extending through an opening in the side wall of the hammer body 32. The extension lugs 84 are engaged by the crank arm 66 which resets the lifter pad 50 (previously described) so that the gauging fingers 78 are moved upwardly and reset to their extended position above the uppermost end of the hammer blade 30 on the donwstroke of the hammer assembly 29. Thus, both the lifter pad 50 and the gauging fingers 78 are reset simultaneously. The crank arm 66 carries a horizontal, grooved bar 85 to engage the two extension lugs 84 and the single extension lug 56.

The aforementioned cylinder-piston assembly 44 comprises a reciprocal cylinder 90 having a lower stem 92 functioning as a crank rod and suitably journaled at its bottom end to the crank 46 of the crankshaft 48. A piston 94 which is disposed in the bore of cylinder 90 fixedly carriers a rod 96 slidable in a bore in the cylinder stem 92 and having its lower end terminating in said bore. The upper part of the piston 94 has fixed thereto a support block 98 which extends upwardly of the cylinder 90 where it terminates in a lug 100 which extends loosely into a cavity 102 formed in the lower part of the hammer slide 36. The support block 98 is connected for relative pivotal movement to the hammer slide 36 by a pivot rod 104 which is mounted in the hammer slide 36 and passes through a bore in the lug 100. It will be apparent that the rotating crankshaft 48 is operable to reciprocate the cylinder 90 and that the piston 94 is slidable in the bore of the cylinder 90 and pivotally connected to the hammer slide 36.

The upper end of cylinder 90 is closed by a cap 106 having an internal bore 107 which forms a slide bearing for the block 98, and also having a flange 108 secured to the top of the cylinder 90 by screws 110. The cap 106 includes a collar 112 extending into the upper part of the bore of the cylinder 90 whereby the lower face of the collar 112 is adapted to abut the upper face of the piston 94.

The lower end of the cylinder 90 is in continuous communication with a pressurized fluid via inlet passage 114 (FIG. 3) so that the pressurized fluid acts on the lower face of the piston 94 to bias or urge the latter in an extended position. Suitable piston rings 116 are provided to seal the pressurized fluid in the lower part of the cylinder below the piston 94. The upper part of the cylinder 90 is vented by a passage 118 in the cap 106.

As the crank 46 passes bottom dead center and commences its upward stroke, the cylinder 90 starts to rise. The piston 94 also rises because the fluid pressure acting on its lower side urges it into abutting relationship with the lower face of the collar 112 of cap 106. The cylinder 90 is carried laterally to some extent as it rises because of its being journaled to the crank 46. However, the hammer slide 36 lifts vertically on the guide rods 40, the differences in motions being accounted for by relative pivotal movement about the pivot rod 104.

Assuming, by way of example, that the apparatus has been set for a dwell period of degrees, i.e. the hammer blade 30 is to remain in contact with the lap seam from 50 degrees before to 50 degrees after top dead center of travel of the crank 46. As the crank 46 approaches 50 degrees before top dead center, the hammer blade 30 contacts and closes the side seam and comes to rest in the FIG. 2 position at 50 degrees before top dead center. After the crank 46 passes 50 degrees before top dead center, the hammer assembly 29 remains in that position of dwell as the cylinder 90 continues torise and carries the collar 112 out of abutment with the piston 94. The hammer assembly 29 remains in the FIG. 2 dwell position until the crank 46 passes over top dead center and reaches 50 degrees past top dead center at which time the bottom face of the collar 112 will have been returned to a lower position to reengage the piston 94 and pull the latter and the hammer assembly 29 downwardly until it returns to the FIG. 1 position of bottom dead center where the cycle is ready to be repeated on a new can body B which has in the meantime entered the bumping station to replace the one just closed. During the whole of this dwell period, the hammer blade 30 remains in pressured engagement with the side seam by virtue of the air pressure in the cylinder 90 which is exerting a constant upward pressure against the piston 94.

In order to vary the number of degrees of dwell, means are provided to change the relative position between the hammer body 32 and the hammer slide 36. In the illustrated embodiment, this is accomplished by providing shims 120 in the bottom of the slot 35 in the hammer slide 36 on which the base of the hammer body 32 sits. The total thickness of the shims 120 may be changed by loosening the clamping screws 33, lifting or removing the hammer body 32 from the slot 35 in the hammer slide 36, increasing or reducing the number of thickness of shims 120 in the slot 35 of the hammer body 32, replacing the hammer body 32 so that its base sits on the shims 120, and tightening the clamping screws 33. It will be apparent that greater total shim thicknesses 120 will increase the dwell because the hammer blade 30 will be closer to the mandrel 10 at bottom dead center of the crank 46 and, therefore, will be brought into contact with the can body sooner (i.e. with less rotational travel of the crank 46 past bottom dead center) than the case where lesser shim thicknesses 120 are employed. Conversely, the thinner the shims 120, the less the dwell period.

As previously indicated, a source of compressible fluid (e.g. air) is in constant communication with the lower part of the cylinder 90 to maintain the hammer blade 30 in pressured contact against the side seam. The air may be supplied via a flexible hose 115 (FIG. 3) from a cushioning or supply tank 137 which is kept replenished, as may be required, by an air compressor 138 through a conduit having a one-way valve 140 therein. Controls such as a pressure regulator valve 139 may be employed to establish the desired pressure in the supply tank 137 and to maintain a substantially constant air pressure therein. Limiting and safety controls such as the relief valve 141 are provided as may be deemed suitable. The air supply tank 137 is sufficiently large, relative to the cylinder 90, so that displacement of the piston 94 during the bumping-cycle operation will not materially vary the pressure in the pneumatic system.

It is desirable that the force with which the hammer blade 30 is held against the lap seam during the dwell period remain substantially constant. Too great a pressure might tend to squeeze out the adhesive A from between the lap seam while insufficient pressure may impair proper seam formation. It will be observed that, during the dwell period, when the hammer blade 30 is in contact with the lap seam, the cylinder 90 moves up and down slightly relative to the piston 94 (compare FIGS. 1 and 2). As the cylinder 90 moves up relative to the piston 94 during the first half of the dwell period, a quantity of air will be displaced from the lower portion of the cylinder 90 through the connection 114 to the'airsupply tank 137. However, the volume of air displaced during this period is small relative to the overall volume of the air system which includes an air-supply tank 137. For example, when the overall cubical-content ratio between the cylinder 90 and the air-supply tank 137 is 350 to 1, and there are sufficient shims 120 to produce a 100- degree dwell, the volume of air displaced by the piston 94 during the first half of the dwell period relative to the volume of the supply tank would be approximately 2800 to 1. Because of the relatively small volumue of air displacement during the dwell period, the air pressure in the system, including that under the piston 94, and the resulting force acting on the hammer blade 30 will remain substantially constant over the entire dwell period. For the same reason, varying the thickness of the shims 120 will not adversely affect the capability of the apparatus to provide substantially constant air pressure during the dwell period.

The hammer assembly 29 and the cylinder-piston assembly 44 may be adapted to handle different diameter can bodies by substituting a cap 106 having a collar 112 of a different longitudinal or axial length. Thus, for a smaller diameter can formed on a smaller diameter mandrel, the longitudinal length of the collar 112 would be shorter than that shown so that the highest attainable position of the hammer blade 30 will be closer to the center line of the mandrel. With each change in collar length, the thickness of shims 120 can be varied to obtain the desired dwell in terms of degrees of crankshaft travel.

It will be observed that the mandrel spline 20 has longitudinal cooling passageways 120 therein, and the hammer blade 30 has a transverse cooling passage 124 communicating at its ends with inlet and outlet passages 126, 128 partially formed in laterally projecting parts 130, 132 of the hammer blade 30. The cooling passages in the spline 20 and hammer blade 30' are adapted to circulate a cooling medium (e.g. refrigerated brine) at temperatures (e.g. sub-zero) to facilitate rapid cooling of the adhesive A as previously mentioned. As best shown in FIG. 5, the hammer body 32 has vertical cut-outs 134 to accommodate the projecting parts 130, 132 on the hammer blade 30 as the latter is cycled up and down relative to the hammer body 32. Suitable flexible hoses 136 may be connected to the cooling-medium inlet and outlet on the hammer blade 30.

Although the illustrated embodiment is concerned primarily with a cemented lap seam can, it will be understood that it may also be used for other types of containers and seams. Thus, as may be found desirable, it may be used on the more conventional soldered sideseam can bodies. It will also be understood that other compressible fluid media may be used in the cylinderpiston assembly 44 and that, alternatively, a hydraulic system having an air-cushioning means (not shown) may be employed to obtain the same results.

As an alternate embodiment (not shown), the cylinder 90 and piston 94 may be interchanged so that the piston 94 is connected to the crank 46 and the cylinder 90 to the hammer slide 36.

It is thought that the invention and many of its attendant advantages will be understood from the foregoing description, and it will be apparent that various changes may be made in the form, construction, and arrangement of parts of the apparatus mentioned herein and in the steps and their order of accomplishment of the method described herein, without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the apparatus and process hereinbefore described being merely a preferred embodiment thereof.

I claim:

1. A machine operable cyclically to make can bodies and the like, the combination comprising a mandrel for successively receiving and supporting partially formed one-piece cylindrical can bodies having radially spaced and overlapping longitudnial marginal edge portions:

bumping means;

means for cycling said bumping means into engagement with said can body; and

dwell means interposed between said bumping means and said cycling means to provide for sustained engagement of the bumping means with the closed side seam;

said dwell means comprising a cylinder having a bore;

said cylinder having a stem;

means operatively connecting said stem to said cycling means whereby the cylinder is reciprocated by said cycling means;

a piston operable in said cylinder;

means limiting the maximum extended displacement of said piston in said cylinder;

a support block fixed to said piston and extending outside of said cylinder;

means pivotally mounting said support block to said bumping means; and

means communicating said cylinder with a source of pressurized fluid whereby the piston is urged and maintained in its extended position against said limiting means to follow the reciprocal movement of said cylinder except during said sustained engagement when the reciprocal movement of the piston is temporarily stopped and the reciprocal movement of the cylinder continued, the difierences in the aforesaid movements being accounted for by relative movement between piston and cylinder.

2. A machine for making can bodies and the like as set forth in claim 1 which includes means to vary the position of said limiting means and thereby provide for adjusting the maximum extended displacement of the piston in the cylinder to facilitate adapting the machine for handling different diameter can bodies.

3. A bumping mechanism for pressing the overlapping longitudinal marginal side seam portions of partially formed tubular can bodies against an internal support to form them into side seams, comprising:

bumping means for contacting said side seam portions,

actuating means having a forward and a return stroke for actuating said bumping means through a forward and a return stroke, and

connecting means for operatively connecting said bumping means and said actuating means,

said connecting means comprising fluid pressure means for maintaining said bumping means in fully extended relationship relative to said actuating means to initiate contact between said bumping means and said side seam portions prior to the completion of the forward stroke of said actuating means and for thereafter permitting relative motion between said :bumping means and actuating means to maintain a substantially constant pressure between said bumping means and said side seam portions during a dwell period which comprises the final portion of the forward stroke of said actuating means and the initial portion of the return stroke of said actuating means until such time as the bumping means and actuating means retain their fully extended relationship.

4. The bumping mechanism of claim 3 wherein said fluid pressure means include a piston,

a cylinder, and

means for maintaining compressed air at a substantially uniform pressure within said cylinder at all times during the operation of said actuating means.

5. The bumping mechanism of claim 4 wherein said piston is associated with said bumping means and said cylinder is associated with said actuating means.

6. The bumping mechanism of claim 4 wherein said piston is maintained in fully extended position against a stop member in said cylinder by said compressed air both before and after, but not during, said dwell period.

7. The bumping mechanism of claim 3 wherein said bumping means is mounted on a slide.

8. The bumping mechanism of claim 3 wherein said bumping means includes a bumping hammer which is chilled by a circulating cooling medium to remove heat from said side seam portions during said dwell period.

References Cited UNITED STATES PATENTS RICHARD J. HERBST, Primary Examiner US. Cl. X.R. 

